Influence mechanism of flow rate on gas-water two-phase flow in hydraulic propped fractures.

This article focuses on the influence of gas injection flow rate on gas-water two-phase flow characteristics in hydraulic propped fractures relevant to coalbed methane (CBM) production. Through physical experiments and numerical modeling, it demonstrates that increasing gas injection rate initially improves gas displacement efficiency and reduces residual water saturation, but beyond a critical flow rate, viscous fingering occurs, destabilizing the gas-water interface and reducing permeability and conductivity of the propped fracture. The study establishes a fingering mathematical model showing that excessive relative migration velocity at the gas-water displacement front, caused by high injection rates, is the fundamental cause of viscous fingering rather than porous media heterogeneity. These findings highlight the importance of controlling drainage flow rates to optimize CBM well productivity and avoid reduced gas recovery due to unstable displacement patterns.