Research On Downhole Compression Algorithms For Acoustic Logging Data

In recent years,the detection characteristics of acoustic logging have developed rapidly in radial,circumferential and axial dimensions.The data volume of 3D acoustic logging tool is increasing,and existing cable real-time transmission mode can not meet the demand,which seriously affects the logging speed and work efficiency.Using downhole compression method can alleviate this problem.In this paper,data characteristics of the single-channel full waveform in remote detection acoustic logging are extracted,such as the time domain and frequency domain.On this basis,the compression method is preliminarily selected,and the downhole data compression platform based on DSP is built.The downhole module and upper computer module of two compression algorithms(DPCM and wavelet transform)are developed.They are tested by experimental logging data,and their compression rate,memory usage,compression time and distortion are evaluated.The expected application effect is analyzed,and the following conclusions are obtained: 1)The compression rate of DPCM algorithm is about 50%,the relative distortions at the peak of the full waveform,the first peak of the direct wave and the reflected wave are all within 3%,the execution time and the memory usage are within the acceptable range;2)The compression rate of one-layer wavelet transform is 50.15%,the distortions at the peak of the full waveform,the first peak of the direct wave and the reflected wave are all within 5%.The compression time and memory usage are small,which is expected to play a greater role in practical applications.The compression rate of the three-layer wavelet transform reaches 12.8 %,but its spectrum and energy distortion are large.The parameters of two-layer wavelet transform are between the one-layer and the three-layer wavelet;3)By combining the one-layer wavelet transform and DPCM algorithm,the compression rate can be further improved with little distortion change and acceptable incresed compression time.This work can provide a solution to alleviate the low cable transmission in 3D acoustic logging,and serve to cost reduction and efficiency increase in logging operation.