Quantitative Logging Characterization Method for Favorable Lithofacies of Tight Sandstone in the Lianggaoshan Formation, Northern Sichuan Basin

Summary To establish the connection between lithofacies and favorable reservoirs in tight sandstone and to guide horizontal well layer selection and productivity evaluation, we propose a quantitative lithofacies characterization method that integrates conventional logging and electrical imaging logging. The core innovation of this method lies in the construction of a lithofacies evaluation workflow based on “lithology + structure.” Taking the tight sandstone of the Lianggaoshan Formation in the northern Sichuan Basin as an example, we first addressed the significant overlap between silty mudstone and argillaceous siltstone in conventional crossplots by utilizing static image conductivity spectrum data to achieve rapid discrimination of sandstone and mudstone in the overlapping zone, thereby improving the accuracy of traditional lithology identification. For rock structure characterization, we used the vertical projection slicing technology of electrical imaging and used a sliding window method to statistically analyze the number of peaks and valleys in the average conductivity curve of slice images, generating a curve that quantitatively represents rock structure. We introduced relative bedding density as a continuous quantitative parameter to characterize the complexity of rock structure. The quantitative features were analyzed using the K-means clustering algorithm and calibrated with core photos to establish an objective classification standard for rock structure. On this basis, adopting the lithology + structure classification scheme, the fine sandstones in the study area were divided into four lithofacies of high-resistivity massive fine sandstone, low-resistivity massive fine sandstone, bedded fine sandstone, and laminated fine sandstone. By comparing the differences in core physical properties among different lithofacies and integrating actual drilling and logging data, low-resistivity massive fine sandstone and bedded fine sandstone were identified as the favorable lithofacies in the study area. This method has achieved good application results in the exploration and evaluation of tight sandstone in the Lianggaoshan Formation of the northern Sichuan Basin, providing valuable guidance for horizontal well layer selection.