Dynamic Threshold Pressure Gradient in Water-Bearing Tight Gas Reservoirs: Experimental and Modeling Insights

Gas–water two-phase flow within such formations exhibits pronounced nonlinear characteristics, significantly affecting fluid transport behavior. To investigate the dynamic threshold pressure gradient (TPG)—which varies with water saturation and permeability during production—this study conducts high-pressure, high-temperature two-phase flow experiments on representative Type I and Type II tight sandstone cores using the pressure difference–flow rate method.

The experimental results demonstrate that TPG is strongly influenced by both water saturation and permeability, with clear distinctions observed between the two reservoir types. Specifically, critical water saturation thresholds marking the onset of measurable TPG were identified as 28.67% for Type I and 15.15% for Type II. TPG exhibits a power-law increase with water saturation, rising sharply when saturation exceeds 40% in Type I and 30% in Type II.