The deviation of gas permeability and classical theory in tight reservoir cores with high pressure

Permeability is an important parameter that characterizes fluid flow through porous media. The widely accepted Klinkenberg (1941) slippage theory was proposed to determine permeability. However, for tight reservoir cores, recent studies have shown deviations in lower back pressure (0.1-7 MPa). This study uses the latest gas flow meter, which expands the measurement range from 0.1 MPag to 40 MPag, to identify the changing curve of the steady-state permeability measurements on tight core at high back pressure. Nitrogen gas permeability of different cores with a wide range of dominated throat radius (0.0605 μm-2.15 μm by high-pressure mercury injection experiments) is measured under the condition of the same 0.4 MPag differential pressure and different back pressures. Results show that when the dominated throat radius is more than 1.0382 μm, the permeability curve conforms to the Klinkenberg slippage theory even when the back pressure is between atmospheric pressure and high pressure. When the dominated throat radius is less than 0.7188 μm, the permeability curve measured in ambient back pressure remains in the realm of the slippage theory; by contrast, the high back pressures do not. The deviation initially increases and then stabilizes as the back pressure gradually increases. Moreover, the gap is enlarged when the core is tight.