Integrated geological quality evaluation using advanced wireline logs and core data: a case study on high clay shale oil reservoir in China

Abstract In the unconventional energy sector, shale oil is increasingly recognized as a crucial supplement to production. In recent years, China has made significant advancements in the development of shale oil. A unique type of pure shale reservoir in the Songliao Basin, distinct from established shale oil reservoirs worldwide, has emerged as a focal point for exploration and research endeavors. This kind of shale exhibits enhanced heterogeneity, high clay content, intricate rock electricity relationship, posing significant challenges to formation evaluation. This study introduces conversion coefficients for the elements and minerals, a decision tree model, a variable T2 cutoff value method, and 2D NMR cluster analysis, all based on the integration of microimaging, spectroscopy, and 2D NMR logging. These novel approaches facilitate a comprehensive geological quality evaluation of key parameters, including mineral composition, lithology, effective porosity, total organic carbon content, fluid composition, and saturation characteristics within pure shale formations from the Songliao Basin. The established petrophysical model has been validated by core analysis data and successfully applied in exploration wells. Through systematic petrophysical analysis, the optimal landing point for horizontal wells was identified based on the identification of the best reservoir quality interval with high movable oil and oil saturation. The subsequent drilling of horizontal wells demonstrated the reliability of petrophysical evaluation in terms of oil production. This integrated evaluation method for pure shale holds reference significance for similar shale reservoirs in other blocks in the future.