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Abstract Revitalizing and sustaining production in mature fields requires a comprehensive technical approach that combines operational optimization with detailed reservoir surveillance. In fields with multiple stacked thin reservoirs, a key challenge is identifying productive hydrocarbon zones (pays) that remain undepleted. This study focuses on a structured workflow for reservoir evaluation, aimed at identifying bypassed pay zones in legacy wells to enhance production and increase recovery. A multidisciplinary methodology was developed, integrating geology and petrophysics to improve reservoir characterization. The approach is based on the interpretation of pulsed neutron logs (PNL) to estimate three-phase fluid saturations in complex geological settings. Various PNL techniques, including Sigma, Inelastic, Capture count ratios, and Carbon/Oxygen, were analyzed to assess their applicability in different reservoir conditions. This workflow was applied to four legacy wells as part of the 2024 Workover campaign, supporting reactivation plans. A comparative analysis of each PNL method and their associated uncertainties was conducted to determine optimal application criteria. Preliminary test results demonstrated positive outcomes, confirming the effectiveness of the workflow in identifying bypassed hydrocarbons. Sigma measurements were particularly effective for hydrocarbon saturation analysis in high water salinity environments (>300,000 ppm), while Carbon/Oxygen methods, typically used in low-salinity formations, showed limitations in these low porosity reservoirs. The integration of PNL data with conventional formation evaluation techniques led to the identification and subsequent testing of candidate intervals in the study wells. These results demonstrated its value as a foundation for future surveillance and reactivation strategies in similar mature field settings. The testing of these intervals confirmed the presence of producible hydrocarbons, demonstrating the effectiveness of advanced surveillance techniques in reactivating old wells with untapped production potential. This study presents a structured and integrated approach for applying PNL technology in complex mature reservoirs, demonstrating how a combination of advanced logging techniques and traditional formation evaluation can optimize production. The findings contribute to refining best practices for reservoir surveillance and well reactivation in mature fields, offering valuable insights for future applications in similar geological settings.