Development Of High-Sensitivity And Broadband Interwell Receiver And Acquisition System

As a kind of geomagnetic detection,the cross-well electromagnetic detection method can effectively overcome the limitations of detection depth and resolution.The cross-well electromagnetic method refers to transmitting and receiving detection signals separately in multiple(at least two)wells that are hundreds or even thousands of meters apart.Based on the electromagnetic waveform information extracted by the receiver,the stratigraphic information can be caculated.The cross-well receiving and acquisition system developed in this thesis detects low frequency signals with the range of 5Hz?2000Hz.According to the electromagnetic field theory,when the electromagnetic wave signals passes through the strata,the electromagnetic wave signals collected by the receiver contains the radial component and the axial component,and these two components must carry the complex parameters information of the strata between wells.Therefore,the complex parameter information of the strata can be obtained by calculating the relevant parameters of the electromagnetic wave signals at the receiving end.In actual detection,due to the skin effect of electromagnetic waves propagating in the strata,large attenuation will occur.Therefore,the signal received by the receiving sensor is extremely weak,and the input signal voltage of the receiver is only u V or even n V level.In addition,the electromagnetic transmitting and receiving ends between the wells are far apart,and the circuits at both ends do not have homologous crystal.Then the frequency difference will accumulate over time,and it will appear as a signal phase difference at the receiving end,that is,the phase of the received signal is different from the actual value.For the above difficulties,the requirements for the receiving and acquisition system are put forward,(1)It must have high-resolution and high-precision receiving and acquisition performance,(2)It must ensure that the circuits at the receiving and transmitting ends can realize the synchronous trigger function.Based on the sensitivity index of the receiving and acquisition system and related theories,firstly,this thesis uses Altium Designer circuit software and TINA to design and simulate the preamplifier circuit and the active filters,and then selects the op amp devices and ADC,power modules,communication modules that can meet the requirements.Secondly,this thesis expounds the principle of phase-sensitive detection,and the relevant parameters of Digital Phase Sensitive Detection(DPSD)algorithm are simulated and determined by Matlab programming software,and then implemented based on FPGA.Thirdly,in the design of the synchronization circuit for electromagnetic detection between wells,based on the GPS timing pulse signals,this thesis realizes the synchronous system with seven-core and four-core cables under wells.In the follow-up,the physical debugging of the receiving and acquisition system is completed,and the sensitivity test of the system is completed under the closed-loop condition in the laboratory,that is,the sensitivity is better than 10 n V in the frequency range of 5?2000Hz.Finally,in the field standard logging site,the actual logging and 307-meter distance experiment were completed,and the measured data contained valid information.Then the four-core and seven-core synchronization experiments have been completed.The phase synchronization error is about 0.1% under the radian scale,and the experimental data is in good agreement with the simulation result.