A frequency adaptive circuit for downhole prospecting

Abstract

This invention belongs to the field of analog integrated circuit technology, specifically relating to a frequency adaptive circuit for downhole detection. This invention utilizes a closed-loop adaptive feedback mechanism, employing multiple excitation frequencies generated by a frequency generator to continuously match and adapt to the transducer's resonant frequency. When a set of excitation frequencies achieves the highest matching degree with the resonant frequency, the echo energy reaches its peak. The frequency generator is adaptively adjusted based on the excitation frequency corresponding to the maximum peak signal obtained during the detection phase, and this optimal excitation frequency is used to generate the excitation signal in subsequent operations, thus completing the adaptation between the excitation frequency and the resonant frequency. This invention effectively avoids the influence of downhole temperature and pressure changes on the transducer's resonant frequency, and combines high automation, good real-time performance, and high imaging quality.

Description

Technical Field

[0001] This invention belongs to the field of analog integrated circuit technology, specifically relating to a frequency adaptive circuit for downhole detection, which combines high automation, good real-time performance and high imaging quality. Background Technology

[0002] Downhole exploration is a crucial part of oil and gas production and resource development. It utilizes the basic principles of ultrasonic imaging, where a transmitting circuit generates a fixed excitation frequency to excite a transducer and transmit ultrasonic waves downhole. The receiving circuit processes the reflected echoes to achieve downhole imaging.

[0003] Because transducers emit ultrasonic waves through their own resonance, the frequency and amplitude of the emitted ultrasonic waves will change when the excitation frequency they receive is inconsistent with their own resonant frequency. Traditional downhole detection devices suffer from the problem of transducer resonant frequency varying with temperature and pressure: during downhole detection, the temperature and pressure experienced by the device change with increasing downhole distance, thus affecting the transducer's resonant frequency. Since the excitation frequency of traditional downhole detection is fixed, a mismatch between the resonant frequency and the excitation frequency will occur during detection, and this difference is unpredictable, severely affecting the ultrasonic signal and compromising imaging quality.

[0004] In summary, existing downhole detection methods suffer from a problem where the transducer resonant frequency varies with downhole temperature and pressure, leading to a mismatch between the excitation frequency and the resonant frequency, which severely affects imaging quality. Summary of the Invention

[0005] To address the aforementioned problems or shortcomings, this invention provides a frequency adaptive circuit for downhole detection, which solves the problem that the resonant frequency of the transducer changes with downhole temperature and pressure in existing downhole detection methods.

[0006] A frequency adaptive circuit for downhole detection (as shown in the attached diagram) Figure 1 As shown in the figure, it specifically includes a frequency generator, a high-voltage pulse generation circuit TX, a transducer, a high-voltage switch S, an analog front-end circuit AFE, an analog-to-digital converter ADC, and a peak detection module.

[0007] The output of the frequency generator is connected to the input of the high-voltage pulse generation circuit TX, and the output of the high-voltage pulse generation circuit TX is connected to the transducer and the high-voltage switch S; the frequency generator generates f. min ~f max Multiple excitation signals of different frequencies.

[0008] The high-voltage pulse generation circuit TX outputs excitation pulses of different frequencies to the transducer according to the input excitation signal.

[0009] One end of the transducer is connected to the output of the high-voltage pulse generation circuit TX and the high-voltage switch S, while the other end is grounded. Each excitation frequency will excite the transducer and subsequent circuits to work, resulting in an echo peak value.

[0010] The other end of the high-voltage switch S is connected to the input of the analog front-end circuit AFE; the output of the analog front-end circuit AFE is connected to the input of the analog-to-digital converter ADC, and the output of the analog-to-digital converter ADC is connected to the input of the peak detection module; the output of the peak detection module is fed back to the frequency generator, and thus the components form an adaptive loop.

[0011] Furthermore, the f min ~f max The fault tolerance range of the transducer caused by temperature and pressure changes in the downhole detection environment of the target well.

[0012] Furthermore, the operating method of the frequency adaptive circuit used for downhole detection is as follows:

[0013] Detection Phase: The frequency generator produces excitation signals of different frequencies. These signals are converted into excitation pulses of different frequencies by the high-voltage pulse generation circuit TX, which can excite the transducer. After being excited by pulses of different frequencies, the transducer emits ultrasonic waves of different energies towards the target object to be imaged. Upon reaching the target object, the ultrasonic waves are emitted back, forming echo signals of different energies. During this phase, the high-voltage switch S is turned off to prevent damage to the analog front-end circuit (AFE) and the analog-to-digital converter (ADC) from high voltage.

[0014] When echoes of different energies reach the transducer, they are converted into electrical signals with different amplitudes. At this time, the high-voltage switch S is turned on. After the electrical signal echoes are amplified by the analog front-end circuit AFE, they are converted into digital signals by the analog-to-digital converter ADC and output to the peak detection module. The peak detection module detects and compares the peak values ​​of the signals based on the digital signals and feeds back the excitation frequency corresponding to the maximum peak signal to the frequency generator.

[0015] Working phase: The frequency generator uses the excitation frequency corresponding to the maximum peak signal obtained in the detection phase to generate an excitation signal in the subsequent working process, thus completing the adaptation between the excitation frequency and the resonant frequency.

[0016] Because the resonant frequency of the transducer changes with temperature and pressure during downhole detection, the excitation frequency and resonant frequency cannot be matched, resulting in inconsistent echo energy. This invention addresses this by using a frequency generator to continuously match and adapt to the transducer's resonant frequency with multiple excitation frequencies. When a particular set of excitation frequencies achieves the highest matching degree with the resonant frequency, the echo energy reaches its peak. The frequency generator is adaptively adjusted based on the excitation frequency corresponding to the maximum peak signal obtained during the detection phase, and this optimal excitation frequency is used to generate the excitation signal in subsequent operations, thus achieving adaptive matching between the excitation and resonant frequencies.

[0017] The principle of this invention is to effectively avoid the influence of downhole temperature and pressure changes on the transducer resonant frequency through a closed-loop adaptive feedback mechanism. This invention uses multiple frequency generators with different frequencies as frequency excitation sources. During use, a self-test process is initiated before each detection interval: firstly, the built-in numerical control scanning module uses a fixed step accuracy at f... min ~f max The frequency generator outputs a frequency within the range, and this clock signal is converted into transducer excitation pulses via a high-voltage pulse circuit. Each excitation frequency excites the transducer and subsequent circuits, resulting in an echo peak. The maximum excitation frequency f is then obtained. max After the peak value is reached, the scan ends. The peak detection module detects and compares the echo peak values ​​corresponding to each excitation frequency to find the optimal excitation frequency, i.e., the excitation frequency corresponding to the maximum echo peak value. This ensures the adaptive matching between the excitation frequency and the resonant frequency, thereby achieving optimal imaging quality.

[0018] In summary, this invention employs a closed-loop feedback mechanism to scan frequencies over short distances. After signal processing by a high-voltage pulse generation and receiving circuit, the optimal excitation frequency is locked, ensuring imaging quality. This invention effectively solves the problem in existing downhole detection systems where the matching of excitation and resonant frequencies is affected by temperature and pressure. Attached Figure Description

[0019] Figure 1 This is a circuit block diagram of the present invention;

[0020] Figure 2 This is a flowchart illustrating the principle of the present invention. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0022] A frequency adaptive circuit for downhole detection, such as Figure 1 As shown, it includes: a frequency generator, a high-voltage pulse generator TX, a transducer, a high-voltage switch S, an analog front-end circuit AFE, an analog-to-digital converter ADC, and a peak detection module.

[0023] In downhole exploration applications, a high-voltage pulse first excites the transducer to generate ultrasonic waves. These waves propagate towards the target object and are reflected back, forming an echo. The echo signal is then converted into an electrical signal by the transducer. Because ultrasonic waves attenuate exponentially in the medium, the received electrical signal is relatively weak. Therefore, the analog front-end circuit amplifies this signal to compensate for propagation attenuation, reducing the dynamic range and facilitating subsequent ADC design and processing. The ADC receives the compensated signal, quantizes it, and outputs digital codewords. The external imaging system then uses these digital codewords to achieve real-time imaging.

[0024] As described in the imaging principle above, the source of ultrasound is the transducer, which is excited by a high-voltage pulse at a fixed frequency. However, in downhole exploration applications, due to the complex mud environment downhole, the temperature and pressure experienced by the transducer are no longer constant with changes in exploration depth, thus affecting its resonant frequency. When the transducer is excited with a fixed frequency, the mismatch between the pulse frequency and the fixed frequency leads to attenuation of the echo energy.

[0025] According to the principles of this invention, a built-in frequency generator is required to generate multiple excitation frequencies: at f min ~f max The system generates excitation frequencies with fixed step precision. Each set of excitation frequencies excites the transducer to produce ultrasonic signals of different energies, which are then processed by the AFE and ADC to obtain a set of codewords. When the frequency range scanning ends, i.e., after obtaining the codeword corresponding to the maximum excitation frequency, the peak detection module processes the multiple sets of codewords and compares them to obtain the largest peak value, i.e., the acoustic signal with the highest energy, which is also the set of excitation frequencies that best matches the resonant frequency. This frequency is fed back to the frequency generator to ensure that the transducer is excited at this frequency during subsequent detection processes, ensuring the optimal operating state of the entire system and obtaining the best imaging quality. The specific operating principle is as follows: Figure 2 As shown.

[0026] As can be seen from the above embodiments, this invention utilizes a built-in frequency generator to control the excitation frequency in real time and, through a closed-loop feedback mechanism, detects the optimal echo peak value in real time, thereby ensuring imaging quality. This method effectively avoids the problem of the matching between the excitation frequency and the resonant frequency being affected by temperature and pressure, which exists in existing downhole detection methods.

Claims

1. A frequency adaptive circuit for downhole detection, characterized in that: Includes a frequency generator, a high-voltage pulse generation circuit TX, a transducer, a high-voltage switch S, an analog front-end circuit AFE, an ADC, and a peak detection module; The output of the frequency generator is connected to the input of the high-voltage pulse generation circuit TX, and the output of the high-voltage pulse generation circuit TX is connected to the transducer and the high-voltage switch S; the frequency generator generates f. min ~f max Multiple excitation signals of different frequencies; The high-voltage pulse generation circuit TX outputs excitation pulses of different frequencies to the transducer according to the input excitation signal; One end of the transducer is connected to the output of the high-voltage pulse generation circuit TX and the high-voltage switch S, and the other end is grounded; each excitation frequency will excite the transducer and subsequent circuits to work, resulting in an echo peak value. The other end of the high-voltage switch S is connected to the input of the analog front-end circuit AFE; the output of the analog front-end circuit AFE is connected to the input of the ADC, and the output of the analog-to-digital converter ADC is connected to the input of the peak detection module; the output of the peak detection module is fed back to the frequency generator, and thus the components form an adaptive loop.

2. The frequency adaptive circuit for downhole detection as described in claim 1, characterized in that: The f min ~f max The fault tolerance range of the transducer caused by temperature and pressure changes in the downhole detection environment of the target well.

3. The operating method of the frequency adaptive circuit for downhole detection as described in claim 1, characterized in that: Detection phase: The frequency generator generates excitation signals of different frequencies, which are converted into excitation pulses of different frequencies that can excite the transducer via the high-voltage pulse generation circuit TX; after being excited by pulses of different frequencies, the transducer emits ultrasonic waves of different energies toward the target to be imaged, and the ultrasonic waves are emitted back after reaching the target to form echo signals of different energies; during this phase, the high-voltage switch S is turned off. When echoes of different energies reach the transducer, they are converted into electrical signals with different amplitudes. At this time, the high-voltage switch S is turned on. After the electrical signal echoes are amplified by the analog front-end circuit (AFE), they are converted into digital signals by the analog-to-digital converter (ADC) and output to the peak detection module. The peak detection module detects and compares the peak values ​​of the signals based on the digital signals and feeds back the excitation frequency corresponding to the maximum peak signal to the frequency generator. Working phase: The frequency generator uses the excitation frequency corresponding to the maximum peak signal obtained in the detection phase to generate an excitation signal in the subsequent working process, thus completing the adaptation between the excitation frequency and the resonant frequency.

4. The method of using the frequency adaptive circuit for downhole detection as described in claim 1, characterized in that: Before each detection interval, a self-check process is initiated: firstly, the built-in CNC scanning module uses a fixed stepping accuracy at f... min ~f max The frequency generator outputs a frequency within the scanning range, and this clock signal is converted into transducer excitation pulses via a high-voltage pulse circuit. Each excitation frequency will excite the transducer and subsequent circuits to work, resulting in an echo peak value. The maximum excitation frequency f is then obtained. max After the peak value is reached, the scan ends; The peak detection module detects and compares the echo peak values ​​corresponding to each excitation frequency to find the excitation frequency corresponding to the maximum echo peak value. The frequency generator uses the excitation frequency corresponding to the maximum peak signal obtained in the detection stage to generate an excitation signal in subsequent operations.

Images