The Design Of Near Probe And High Resolution Measurement Circuit Of 3D Acoustic Logging Tool

With the development of logging technology,three-dimensional sonic logging has become an important logging method.Its measurement principle is to analyze the physical characteristics changes such as amplitude or frequency of the acoustic waves after transferring in different strata.It can be used to study the drilling geological profile,then to assess the quality of cementing.In the actual logging process,because of the high temperature and complication of the logging environment,the acoustic signal to be measured will be affected seriously,so it is necessary to develop a high precision underground measurement system so as to satisfy the increasing accuracy of future logging tool.The three-dimensional sonic logging tool can simultaneously measure multiple azimuth acoustic signal,thus providing radial,axial and circumferential threedimensional geological structure information of strata.Firstly,this thesis introduces the structure,the logging principle and process of the three-dimensional sonic logging.Then,according to the requirements of logging,the high-precision measurement circuit is designed,including the low-noise signal conditioning circuit and the analog-to-digital converter circuit.Three-dimensional acoustic logging tool's high-precision measurement circuit uses the "ADC + FPGA" for the hardware architecture.Its low-noise preamplifier circuit achieves the amplification and filtration of the weak acoustic waves reflected from the strata,which is constituted by amplifying circuit,gain programmable circuit and highpass filter;And the sigma-delta high-precision analog-to-digital converter is based on the theory of that high sampling rate in exchange for high accuracy,converting the input analog signal into digital signal that can be stored and transmitted easily,The serial data high-speed transmission technology achieves real-time transmission of the logging data,and the low-voltage differential transmission technology can reduce the common mode noise interference in the data transmission process effectively.The circuit uses verilog hardware description language to achieve the FPGA's function,including the control of the analog-to-digital converter's sampling process,the storage and transmission of the logging data.Finally,the correctness of the designed high-precision measuring circuit and the stability of the three-dimensional sonic logging are verified through a series of experiments.In the thesis,the flume experiment verifies the implementation of the function of the three-dimensional acoustic logging tool.And the high temperature experiment verifies the system's stability in high temperature.Besides,we can export a large number of analog-to-digital converter's sampling data,which can be used to calculate the converter's effective resolution,and then verify that the high-precision measurement circuit achieves the expected goal of the three-dimensional acoustic logging tool.