| Ultrasonic image logging technology is an important development trend of modern logging technology and is also a key research of logging technology. The speed and result of the former ultrasonic casing imaging tool is excellent in Daqing Oilfield, but its diameter is too large, limit the scope of use. The successful researchment of small diameter eliminates the probability of sticking and blocking by deformed casing. Expanding the scope of the ultrasonic casing imaging tool will have great application potentials in logging field of oilfield.The character of small diameter ultrasonic image logging system and the logging tool,structure,working principle of surface data acquisition system belong to small diameter ultrasonic imaging system were analyzed in this paper. System requires the ultrasonic imaging of the collected images lossless compression. Several commonly used lossless compression methods were introduced in this paper, such as Huffman coding, Arithmetic coding, LZW coding and widely used coding-based predictive coding theory, compression, scope of application and limitations. The effects and the limitations were analyzed. This paper focused on the application of"Adaptive Predictive Coding based on Image Segmentation"in the small diameter ultrasonic casing imaging systems. By programming, the algorithm was achieved on the ADSP-2181. This algorithm, JPEG lossless algorithm and JPEG-LS algorithm were applied to the system. They were used to do the compression experiments of the ultrasonic images collected in the well.The results show that the compressibility of adaptive predictive coding algorithm based on Image Segmentation is much better than these two conventional lossless compression algorithms and the speed of the algorithm is very rapid, besides the complexity is not increased obviously. This lossless compression arithmetic is very suitable to small diameter ultrasonic casing imaging system. |
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