Design Of Signal Processing And Transmitting Ultrasonic Control Circuit In The Circumference Borehole Imaging Logging Tool

It has always been an important research topic to measure the underground oil reserves safely,efficiently in the petroleum industry.The research of fracture is a key aspect in the measurement of downhole oil reserves.In the exploration of logging instruments,acoustic logging is an effective way to detect fractures in open hole.Circumferential Borehole Imaging Logging Tool(CBILT)is a kind of logging instrument mainly used to measure the information of open hole borehole wall.Its basic working principle is to transmit ultrasonic wave in mud when it meets different media and then reflect it.After collecting and processing the echo,the data will be uploaded to the upper computer for analysis by the personnel on the well.This thesis mainly describes the main control and signal processing method,ultrasonic transmitting control circuit and signal storage control of the CBILT.First of all,the development and present situation of ultrasonic imaging logging tool are introduced,and the research significance of ultrasonic imaging logging tool is clarified.Then the basic working principle and structure of the CBILT are discussed,and the goals and requirements that need to be achieved in the thesis are analyzed.Then three aspects of the design are focused.The first aspect of the design is the main control and signal processing.The command receiving module,transmission control module,receiving ADC signal and processing module,uploading data module and signal storage control module are designed and implemented by utilizing the advantages of FPGA that is good at processing high-speed and parallel signals.The second aspect is the design of the circuit used to drive the transducer to emit ultrasonic waves.The transducer needs to be driven by a high voltage of up to ±8 0V and a high frequency signal of 250 k Hz,so the MOSFET driving circuit is designed to drive the transducer,and the vibration damping resistor is designed to eliminate the unnecessary vibration of the transducer.At the same time,the high voltage control shift circuit is added to control the transmitting power.High and low voltage power supply control is designed to reduce working power consumption.Considering that the high voltage part is easy to damage the low voltage circuit once there is a problem,the high voltage sampling circuit to monitor the high voltage is added in this design.The third aspect is the design of signal storage control.When there is data downhole that is not easy to analyze or other unexpected situations occuring,a large number of original signal data needs to be recorded and saved downhole.Therefore,a large capacity memory chip NAND FLASH is added.The NAND flash memory requires a separate control method to complete data access control.The design of the controller is mainly divided into three basic operations: erase,program and read.In the thesis,these operations are designed and implemented,and an ECC check widely used in the industry is designed and implemented.Finally,the circuit designed in this thesis has been simulated and tested in a laboratory environment,and has been installed in the instrument for a system test.The instrument works well.Test and experimental results show that the works of the thesis meet the expected design requirements.