Keywords: 
• Grey cluster /
• Qingshankou formation /
• Automatic distinguishing of lithology and microfacies

Abstract: Based on the study of sedimentary megafacies and subfacies made by former researchers,the authors have studied the automatic distinguishing of lithology and microfacies by grey clus-tering,which is the process of determining decisio一making matrix,white functio equations,cluster weight,and cluster coefficient. In this study,the second sandstone section in the third member of Qingshankou formation of ringtai area in Songliao Basin is taken as an example. First,parameters sensible to lithology such as lateral log (Rt ),sonic moveout (Ac),and natu-ral gammary (ER) and those sensible to microfacies, like thickness of sandstone, rnudstone,and the transitional rocks of these two and the sandstone pereentage,are chosen as the work-ing variables. Second,by studying 9 core holes that are representative to the fades change in Yingtal region,the varying ranges of the logging results to different lithosomes have been ob-tamed with respect to Rt,AC,and ER. The statistical thickness ranges of sandstone, mud-stone,and the transitional rocks and the perentage of sandstone have also been made. Finally,the logs of Rt,Ac,and ER in 60 holes are changed into numerical values by computer in each depth interval of 0. 2 m. And the automatic distinguishing of lithology and microfacies has heen conducted by grey clustering. Three different lithosomes such as sandstone,mudstone,and the transitional rocks (argillaceous sandstone,sandy mudstone ) can be recognized. The distinguishable microfacies by this method are braided river course,channel一mouth har,river island,and sheet bar. The results made by grey clustering are basically the same as those ob-tained by common geoloic analysis.