A new logging evaluation method of oil adsorption by clay minerals for shale oil reservoir based on the Waxman–Smits model

As a critical component of the global energy portfolio, shale oil has garnered considerable attention, making it essential to understand its enrichment mechanisms and controlling factors. However, accurately evaluating the hydrocarbon potential of shale oil reservoirs remains a significant challenge, particularly in quantifying oil adsorption by clay minerals, for which cost-effective and efficient evaluation methods are still limited. In this study, integrated geochemical and reservoir characterization experiments were conducted to investigate the factors controlling oil adsorption by clay minerals in shale reservoirs. Results show that cation exchange capacity ( Q v ) is a key parameter—second only to clay content and specific surface area—in assessing oil adsorption capacity. Based on this finding, the classical Waxman–Smits (W–S) model was improved by incorporating a quantitative relationship between Q v and oil adsorption. The resulting modified W–S model enables rapid, continuous, and quantitative evaluation of oil adsorbed by clay minerals directly from well log data, with predictive accuracy suitable for practical application. This model provides a new approach for evaluating oil adsorption in shale reservoirs and offers practical guidance for reservoir quality assessment, target selection, and optimization of development strategies.