Production Dynamics and Development Optimization in Mature Offshore Oil Fields: An Integrated Development Curve and Shewhart Control Approach

Mature offshore oil fields commonly exhibit declining oil production, increasing water production, deterioration of reservoir performance, and increasingly complex production management requirements. This study presents an integrated production performance assessment of the Darwin Bank, Pirallahi Island, and Gurgan-Deniz offshore oil fields in the Absheron petroleum province of the Caspian Sea using long-term development curves, Shewhart statistical process control (SPC) charts, water cut analysis, water injection history, gas production behavior, and voidage replacement ratio (VRR). Historical production records from the initial development stages to the recent period were analyzed to distinguish long-term production trends from operational and development-related changes. The three fields exhibited substantially different production trajectories. Gurgan-Deniz experienced the most rapid production buildup and subsequent depletion, Darwin Bank showed the most prolonged production history, whereas Pirallahi Island exhibited persistent high water production and complex late-stage redevelopment behavior. The integrated Shewhart analysis identified periods of statistically abnormal oil, water, gas, and water cut behavior, providing an operational framework for identifying changes requiring reservoir management attention. In Pirallahi Island, the recent increase in water injection and an estimated VRR of approximately 1.34 are consistent with active pressure support and redevelopment conditions. Based on the identified production constraints, potential reservoir management measures, including selective water shut-off, well interventions, infill drilling, and appropriately selected enhanced oil recovery (EOR) methods, are identified for further field-specific evaluation. The main contribution of the study is the integration of long-term development curves with Shewhart-based statistical control of oil, water, gas, water cut, and injection behavior to identify production changes and support targeted reservoir management decisions. The proposed framework provides a practical data-based approach for monitoring reservoir performance and supporting the continued development of mature offshore oil fields under data-limited conditions.