Research On The High Resolution Micro-resistivity Imaging Logging Acquisition Circuit

Oil is widely used and its importance is self-evident.However,with the development of oilfield resources gradually entering the middle and later stage,the difficulty of crude oil exploitation is increasing.In order to collect and process downhole information more accurately,it is particularly important to exploit oil with the most ideal means.Electromagnetic wave measurement while drilling technology has the characteristics of high real-time performance,high efficiency,high cost performance and more accurate acquisition of formation parameters,which has gradually become the new trend of logging technology.But,due to the large attenuation of downhole signal,poor signal-tonoise ratio,and the long distance of information transmission,the signal reaching the surface is extremely weak.It is difficult to acquire and process weak signal,which hinders the development of logging while drilling technology.Therefore,it is of great significance to design a logging while drilling equipment to accurately collect and process the weak signals in the well.This paper focuses on the acquisition and processing technology of weak signal,and then designs a high speed and low bit error rate electromagnetic wave MWD system.Based on the higher standard measurement system,high-speed data processing capacity and good control function can not fully meet the engineering needs,accurate weak signal acquisition and processing technology is also essential.Therefore,people are not fully satisfied with the traditional single processor architecture,on this basis,this topic designed a hardware platform based on FPGA and DSP.FPGA mainly completes timing logic and interface design,while DSP mainly carries out complex algorithm processing.The scheme has the advantages of flexible structure,strong universality and convenient modular design,which can save algorithm resources,improve the calculation rate and save the development cycle.Moreover,the framework platform is simple to update and maintain,so it is very convenient to be applied to the real-time data information processing system in the mine.Multipath propagation,as a key feature of wireless channel transmission,makes the received signals overlap with each other,resulting in Inter-symbol Interference(ISI).However,OFDM transmission system divides all channels into orthogonal sub-channels in the frequency domain,resulting in orthogonality between the carriers and superposition of spectrum between them.On the one hand,interference between sub-channels is reduced,and on the other hand,spectrum utilization is increased.Therefore,OFDM technology and RS coding with strong error-correcting ability are used for information transmission in the well.This coding method can eliminate the OFDM symbol of peak average ratio,achieve low bit error rate transmission,and realize the stability and reliability of high-speed transmission system.In order to control the downhole system more accurately,the bidirectional transmission system of sending control instructions from the surface and uploading information from the downhole is adopted to realize the realization.Issue a simple control command,can use low bit error rate and stable and reliable DBPSK technology,baseband transmission using simple AMI code.Finally,a high speed weak signal acquisition and processing board is designed.Under the electromagnetic measurement while drilling system,the whole machine is adjusted smoothly.After that,the field test was carried out in Yanjiao Base of CNOOC.According to the analysis and processing of the experimental results,the acquisition and processing board can work stably and reliably for a long time,which verifies the basic requirements of the design expectation.