Rate allocation optimization for edge-water gas reservoirs using a streamline-based mobile water–gas ratio

Strong heterogeneity and active aquifer support of most natural gas reservoirs in the Sichuan basin, China, pose significant challenges for maintaining stable gas production, including early water breakthrough and rapid pressure depletion. Optimal rate allocation is essential for an edge-water gas reservoir to maximize gas recovery while controlling water production. This study introduces a novel derivative-free rate allocation optimization method that enhances gas recovery and reduces water production by adjusting well rates based on a streamline-based mobile water-gas ratio. The entire optimization period is divided into multiple user-defined time intervals, and the optimization process is carried out sequentially. Within each interval, the ratio of mobile water production to gas recovery is calculated at both the well and field levels. These ratios are then used to generate well rate multipliers, which iteratively update the rate allocation. Once an optimal interval is completed, the process moves to the next, continuing until the end of the field life. The effectiveness of the proposed approach is demonstrated using a sector model and further applied to a large-scale edge-water gas reservoir in the Sichuan Basin, China. These results indicate that the streamline-based approach successfully optimizes well rates under field rate constraints, increasing gas recovery while reducing water production. Increasing the gas drainage volume, as represented by time-of-flight to the producer, is identified as a key mechanism for minimizing residual gas.