Statistical analysis and evaluation of lithofacies from wireline logs over Beleema field, Niger Delta, Nigeria

摘要

A statistical analysis of well-log data for the purpose of estimating and evaluating lithofacies with depth, around ‘Beleema’ field, Niger Delta, was carried out. The principal component analysis (PCA) technique and the bulk volume water and the grain size relationships formed the main principles of analysis. The PCA was applied to selected lithology-sensitive logs, each serving as a variable within the trivariate statistical system. It involved determining the first principal component (PC1) in each well, plotting them against depth and segmenting into intervals with similar statistical characteristics. The gamma ray log was used as control for the segmentation. A total of forty-three (43) electrofacie-blocked units, grouped into two major facies - sand and shale (major) - as well as two shaly-sand and sandy-shale (minor), were identified within the wells studied. Also, the bulk volume water (BVW) was observed to vary from 0.0224 in coarse grained sand facies to 0.0892 in silt grained sand facies. The grain size values obtained varied from about 0.0625 mm in silt grained facies to a range of 0.5 to 1.0 mm in coarse grained facies. The computed BVW curves closely mimic the field gamma ray traces; such that the former could be confidently employed where the latter is unavailable.