Elemental Characteristics and Lithofacies Well-Logging Response Features of Mixed Sedimentary Rocks in the Lower Section of the Upper Ganchaigou Formation in the Gasikule Oilfield

The lower section of the Ganchaigou Formation in the Gasikule Oilfield is a mixed sedimentary system where terrigenous clastic rocks and carbonate rocks occur in interbedded or intercalated forms. The mineral and rock types are complex and diverse, making lithological identification extremely challenging. Currently, development efforts primarily focus on favorable clastic rock reservoirs, while the identification of carbonate reservoirs remains difficult, severely restricting the recognition and development of favorable reservoirs. To address the issues in the mixed sedimentary system, such as diverse lithologies, similar well-logging response characteristics, and the difficulty in effectively distinguishing clastic rocks from carbonate rocks using conventional well-logging curves, this study primarily employs X-ray diffraction (XRD) analysis and rock scanning logging data analysis, supplemented by thin-section analysis, core description conclusions, and well-logging data. By comprehensively analyzing mineral and rock types, mass fractions, and elemental mass fractions, the study explores the optimal correspondence between mineral element content and rock composition content. The results indicate that silicon content reflects sandy content, while calcium and magnesium contents indicate carbonate content. The clay content is then calculated based on the sandy and carbonate contents. Using a neural network combined with deep learning analysis, typical well-logging curves and rock scanning data are nonlinearly fitted to calculate silicon, calcium, and magnesium contents across the entire region. The sandy and carbonate contents are then calculated through fitting equations, and the clay content is derived by combining the carbonate and sandy contents. The calculated rock compositions are normalized to establish a classification standard for mixed sedimentary rocks, enabling lithofacies division. This provides a foundation for subsequent research on sedimentary facies and reservoir studies.