Design Of Data Acquisition And Processing Circuit For Cased Hole Ultrasound Imager

The main purpose of the cementing quality inspection is to detect the quality of the cemented surface of the cement ring with the casing and the formation in the casing wells,as well as the state and strength of the surrounding medium,the structure of cement ring,casing state and medium condition,which gives a comprehensive evaluation of the structural condition of the casing wells.The quality of the casing wells determines the subsequent development and production life of the oil and gas wells,so cementing quality evaluation is of great significance.At present,the most advanced cementing quality inspection technology is the casing surrounding medium imaging technology.This thesis designs and implements a casing wells ultrasonic imaging instrument data acquisition and processing circuit.The main contents include hardware circuit,echo signal detection and echo data compression.In the hardware circuit part,according to the function and performance requirements of the instrument,the data acquisition and processing circuit based on DSP+FPGA structure is designed,and the noise performance of the ADC signal chain is analyzed in detail.In addition,the circuit is carried out for the high temperature working environment of the instrument with necessary thermal design being realized and simulated.In the echo signal detection part,considering the echo detection accuracy and the instrument hardware resource limitation,the real-time processing flow of the downhole echo signal is designed,which includes the first wave detection and parameter extraction,the digital filtering of the echo signal,and the automatic gain control of pre-signal conditioning circuit,etc.In the echo data compression part,the characteristics of different types of compression algorithms are analyzed.According to the requirements of logging timing and communication protocol,adaptive differential pulse code modulation and compression algorithm(ADPCM)is selected,and FPGA-based ADPCM encoder and decoder are implemented.The test results show that the data acquisition and processing circuit of the casing well ultrasonic imager can work normally and stably in the temperature range of 25~175 °C.The dynamic performance of the circuit in the design operating temperature range,the echo acquisition of different sensors of different sizes,and the real-time compression of echo data meet the logging requirements and can be applied in practical engineering.