Abstract: In geologic orienting drilling in Well Block Mo-005 of Mobei oilfield in Junggar basin, minimax variance cluster method was applied, and automatic layering data record on digitalizing well logs had been realized. This method can be used to find out maximal and minimal points of interlayer variances on digitalizing well logs as layering points, and take account of screen effect of overlying and underlying surrounding rocks on thin sands or layers along with fluctuation of well log curves. All layering points are put in order as a set of ordinal numbers in terms of depth, followed by performing parallel processing with the method of cluster analysis. The results are very closed to real lithologic section zonation owing to its most distinct interlayer heterogeneity and inner-layer homogenization. The whole procedure of layering data record is automatically fulfilled on the basis of these method with VB (V6.0) program by computer. Such a method is suitable for auto-well logging phase analysis of sand-shale series.

Key words: minimax variance cluster analysis, digital well log curve, auto-layering data