Design Of The Front End Circuit Module Of Circumferential Borehole Imaging Logging Tool

Circumferential Borehole Imaging Logging Tool is mainly used for the scanning imaging measurement of the open hole well and the inner wall of the casing well,and it can also measure the corrosion of the casing.In open hole measurement,it can detect formation fractures,holes and bedding structures,and judge formation by synthesizing azimuth logging information.When the instrument works,it drives an ultrasonic transducer to send ultrasonic wave to the well wall and receive the echo from the well wall.By collecting and calculating the echo signal,we can get two important information: the echo arrival time can reflect the borehole size;the echo amplitude can reflect the borehole lithology.The traditional ultrasonic logging tool uses the method of analog circuit to get the echo time and echo amplitude.However,in the work,this method will bring high false detection and missed detection rate,so the reliability of the instrument needs to be further improved.The new echo signal detection method is adopted in Circumferential Borehole Imaging Logging Tool.The echo signal is collected in full wave train,digitized,and then the echo information is obtained through digital signal processing,which solves the problems of high power consumption and low reliability existing in the traditional ultrasonic logging instrument.The instrument mainly includes the front-end circuit which is responsible for the ultrasonic excitation,transmitting and processing the collected echo,and the main control circuit module which is responsible for the data processing and communication.This thesis focuses on the design of the front-end circuit module of the ultrasonic borehole imager.This thesis first introduces the research background and significance of this thesis and the research status of ultrasonic imaging logging instrument at home and abroad;then introduces the basic structure and working principle of the ultrasonic imaging logging instrument around the well,and according to the requirements of ultrasonic imaging logging,gives the overall design scheme.Then,the design of front-end module is introduced.The front-end circuit module design mainly includes the design of transmitting circuit,echo conditioning circuit,echo acquisition circuit and transducer matching circuit: the transmitting circuit generates high-voltage pulse signal to stimulate the transducer to emit ultrasonic.There are five functional modules in the echo conditioning circuit: channel selection circuit,program-controlled amplifier circuit,bandpass filter circuit,differential amplifier circuit and ADC driver circuit,which are responsible for the conditioning of weak and high noise echo signals.The combination of ADC and FPGA is adopted in the echo acquisition circuit,which is responsible for the full wave train acquisition of the echo signal.The transducer matching circuit is responsible for reducing the tail vibration of the transducer and improving the measurement range and accuracy of the instrument.Finally,the test of the designed circuit is carried out,and the experimental results are analyzed.The results show that the designed front-end circuit module meets the design requirements.