Case Study of Dynamic Stratified Production Allocation and Remaining Oil Evaluation in Offshore Multilayer Commingled Reservoirs with Strong Aquifers

After prolonged development, offshore edge- and bottom-water reservoirs have entered an ultra-high water-cut stage. Under long-time multilayer commingled production conditions, accurate dynamic quantification of layer-wise production remains technically challenging, and conventional production allocation approaches often lack the accuracy required for fine-scale reservoir management. To address these challenges, this study proposes a production allocation method that integrates static reservoir properties, dynamic production performance, and pressure-based correction. The resulting layer-wise allocation provides a quantitative basis for evaluating remaining oil utilization and delineating the distribution of remaining oil across individual layers. The method is formulated on the basis of a pseudo-steady-state productivity model that incorporates wellbore imperfection effects. The initial production rate of each layer is calculated by combining reservoir transmissibility with production pressure drawdown. To account for unequal pressure responses among layers under commingled production—resulting from pressure imbalance, limited edge- and bottom-water energy support, and interlayer interference—a correction factor is introduced to adjust the effective production contribution of low-pressure layers. Compared with the PLT test results, the average error of the conventional KH method was 16.7%, whereas the average error of the proposed method was reduced to 6.1%. The average error was reduced from 16.7% to 6.1%, corresponding to a 63.5% reduction in prediction error, indicating that the proposed approach can provide a more reliable estimation of layered production contribution. The proposed method enables continuous and dynamic production allocation for commingled wells without the need for frequent surveys, offering a practical tool for identifying multilayer production imbalance, evaluating remaining potential, and supporting development optimization in offshore oilfields.