Prediction of Diagenetic Facies Using Well Logs in Tight Sandstone Reservoir - A Case from Chang 7 in Ordos Basin, China

Abstract

Understanding diagenetic heterogeneity in tight sandstones is important for prediction of reservoir quality and further for economic success in hydrocarbon exploration. The seventh member of the Upper Triassic Yanchang formation in the Ordos Basin (Chang 7), central China, is an important oil-producing interval characterized by low porosity and low permeability. This study suggests that diagenetic facies identified from petrographic observations can be upscaled by correlation with log responses, which can facilitate prediction of reservoir quality in field-scale. Four diagenetic facies are determined based on pertrographic features including intensity of compaction, cement types and content, and degree of dissolution. Log characteristics of each diagenetic facies are summarized. However, because of overlaps in all well logs crossplots, it is difficult to discriminate these diagenetic facies. To further delineate these diagenetic facies, principal components are calculated using log values and a better model predicting diagenetic facies based on principal component analysis is built. The model is validated by blind testing log-predicted diagenetic facies against petrographic features from core samples in well Cheng 96, which shows it is a viable predictive model.