Research On Downhole Spectrum Stabilization Algorithm For Elemental Analysis Logging Tool

Formation element logging can give a more accurate description of the strata from the atomic scale,and provide more effective data for the exploration of complex formations;moreover,because of the non-contact measurement,the instrument is little influenced by the outside temperature,pressure and borehole condition or other factors,therefore,it has a wide range of applicability.This thesis reports on the design of elemental analysis logging tool based on pulsed neutron source.The focus is the realization of data processing and transmission.In this paper,the main control & communication circuit is developed for the instrument,and the rule for the generating of the data spectrum is instituted,besides,algorithm used for fixing the energy spectrum in which offset comes about.The main function of the main control circuit is to monitor the working condition of the instrument,process the spectral data and exchange data with the ground system.The circuit is able to achieve 20.83Kb/s data download and 93.75Kb/s data upload.This paper focuses on the EDIB communication,the principle of the circuit and the software realization of Manchester encoding and decoding are analyzed in detail.The test results show that the circuit has good stability and reliability,and can work normally in the environment of 150? for long time,and the packet loss rate is less than 0.03%.The stability spectrum algorithm can effectively correct the offset of the ±10 channels in the case of the 256 total energy channels.By means of controlling the timing of pulsed neutron emission and the timing of signal acquisition and counting,the instrument can get the energy spectrum data consist of 256 energy channels,including the inelastic scattering spectrum,the neutron capture spectrum and the background spectrum;and a time spectrum according to the time when the ? ray signal is generated is achieved at the same time.A periodic signal is used to test the function,and the results are in agreement with the design,which shows that the instrument can correctly distinguish and count the ? ray signals and do the counting under the experimental conditions.However,in the practical logging process,due to high temperature and other factors,the output signal of the components will inevitably drift,which lead to changes of the spectral shape,and has a negative effect on further data analysis,so some adjustment about the measured energy spectrum should be done.In the end of the paper,two algorithms about the spectra-stabilization are proposed: the channel-adjustment algorithm and the energy-adjustment algorithm.In the algorithm of channel-adjustment,the system fixes the channel of the spectrum directly,by segmenting each channel into small parts,the peaks in the adjusted spectrum is wiped out;In the algorithm of energy-adjustment,an extra group of energy-channel reference data is introduced,the energy spectrum can be adjusted indirectly by re-fixing the reference data;the Test results show that both the two algorithms can effectively eliminate the drifts in the energy spectrum.