Comprehensive Prediction Method of Dynamic Reserves of Gas Reservoir Based on Hydraulic Flow Unit Division and New Water Flooding Characteristic Curve

Conventional water-drive characteristic curves are predominantly developed for water-drive oil reservoirs and often exhibit limitations when applied to water-drive gas reservoirs. To address this, this study proposes an integrated methodology specifically designed for water-drive gas reservoirs, combining a novel characteristic curve equation with a gas reservoir classification approach based on the hydraulic flow unit. A new characteristic curve equation is developed by establishing a relationship model between the relative permeability ratio and movable water saturation using the material balance principle. Reservoir classification via the flow zone indicator (FZI) method yields normalized relative permeability ratio curves for different reservoir types, with fitting parameters determined by integrating the new relative permeability ratio model. Dynamic geological reserves calculated by this method are compared with those from the Blasingame method using historical production data of typical gas wells, validating the model’s reliability. The FZI clustering method classifies the target reservoir into six flow units (A–F), with distinct normalized gas–water relative permeability curves reflecting fluid flow capacity. The new relative permeability model demonstrates strong fitting performance, supporting the water flooding characteristic curve equation. The close correlation between dynamic reserves and fitting coefficient bn, FZI values, and permeability further confirms the method’s applicability. The findings establish a robust framework for dynamic reserve assessment in water-driven gas reservoirs and systematic reservoir characterization.