<p>This paper aims to develop a robust mathematical model for real-time skin factor evaluation during acid stimulation treatments in naturally fractured reservoirs (NFRs), addressing the limitations of existing methods that are designed for conventional reservoirs. A novel model is formulated by integrating the pressure transient response of double-porosity systems (based on Kazemi’s approach) into the real-time skin factor evaluation framework. The model modifies Prouvost and Economides’ method to account for NFR characteristics, including storativity ratio and interporosity flow coefficient. Its effectiveness is validated through a case study of a matrix acidizing treatment in an Iranian oil well from an NFR, with comparisons to established methods by Paccaloni, Prouvost and Economides, and Zhu and Hill. The proposed model accurately predicts the ultimate skin factor with only a 1.2% error relative to well test data, significantly outperforming other methods (errors up to 71.1%). This study introduces the first model to incorporate double-porosity pressure transient behavior into real-time skin factor evaluation for NFRs, offering a tailored approach that enhances the accuracy of stimulation treatment assessment and decision-making in complex reservoirs.</p>