Half-coil Induction Logging System Based On DSP And FPGA

With the deepening of oil and gas exploration,horizontal wells and highly deviated wells are more and more used in practical operations.Geosteering technology with remote detection function is the key technology to achieve effective drilling in the target formation.Half loop logging is a new method to realize geosteering while drilling.In this paper,a half coil induction logging experimental system based on DSP and FPGA is designed.It can transmit and receive signals,adjust the angle between source distance and coils,and provide an experimental device for the study of the characteristics of half coil in laboratory.The main research contents and achievements are as follows.The first part completes the analysis of the principle of semi-coil induction logging and the overall design of the experimental system.According to the theory of induction logging,the calculation formula of the receiving voltage of the half coil is derived.The overall structure of the experimental system is designed.The technical specification requirements of the emission and reception module of the semi-coil induction logging experimental system are put forward,as well as the functional requirements of the overall experimental system.The second part is the launch module design of the half coil induction logging experimental system.It includes software design and hardware circuit design.The software design includes the design of the minimum subsystem based on TMS320F28335 to control AD9833 to generate the 20 k Hz sinusoidal signal required by the experiment.The hardware circuit includes DDS waveform generation module,differential amplifier module and power amplifier module.Hardware circuit design includes ad8221 differential amplifier module circuit welding,power amplifier module circuit welding.Ni Multisim Simulation software is used to simulate the differential amplifier module and power amplifier module to verify whether they meet the design requirements.The frequency signal required by the experimental system is generated and amplified to the drive coil load.The simulation results show that the ad8221 differential amplifier can effectively reduce the CMRR.The power amplifier circuit with two-stage amplifier can amplify the current and voltage at the same time.The third part is the design of the receiving module of the half coil induction logging experimental system.Including software design and hardware circuit design.The software part includes FPGA design,ad7606 control through SPI transmission protocol for receiving coil signal high-speed acquisition,data cache and DSP reading.The hardware part includes preamplifier circuit,which is used to amplify the weak signal on the receiving coil;low-pass filter circuit,which uses Butterworth low-pass filter to filter the high-frequency noise;AD acquisition circuit,which is used for discrete signal acquisition on the receiving coil and data communication between FPGA and DSP.The signal receiving module of the experimental system is completed,and the sampling speed is fast and the precision is high.The fourth part is the debugging and result analysis of the half coil experiment system.Firstly,according to the signal flow direction,the transmitter and receiver modules are debugged.Secondly,the overall circuit and software of the whole system are debugged.The debugging results show that the signal transmitting and receiving of the half coil induction logging experimental system is stable and meets the requirements of technical indicators.Then the functional analysis of the experimental system is carried out,including the change of azimuth,source distance and turn number.Finally,the characteristics of coil edge detection are analyzed.The results show that the half coil system is sensitive to azimuth and high conductivity objects,and has a certain edge detection ability,and the received signal strength of the half coil is higher than that of the whole coil.The experimental system has the function of verifying the characteristics of the half coil,including the sensitivity of the half coil to the rotation angle,the sensitivity to the change of the boundary conditions,and the characteristic that the signal receiving strength is greater than that of the whole coil.The effectiveness of the half coil experimental system is verified by various analyses.The characteristics of the half coil are explored in the laboratory.The experimental system has achieved the expected experimental index requirements and functional requirements.