On the flow regime model for fast estimation of tight sandstone gas apparent permeability in high-pressure reservoirs

A flow regime-based gas apparent permeability model in high-pressure tight sandstone reservoirs is established by bridging molecular kinetics, gas transport mechanisms, and apparent permeability. This model is well validated against simulation and experimental data. Results indicate that an equal-flow point tends to move to a low-pressure region with an increase in a pore diameter. As an equal-flow line is close to an isoline of a Knudsen number of 1, a flow regime is divided into three Knudsen number-based regions. Both the equal-flow line and the isoline of a Knudsen number indicate that an increasing temperature expands a Knudsen diffusion-dominated region, which further enhances the gas transport permeability. A typical curve of flow-regime gas apparent permeability provides a fast estimation of gas apparent permeability based on a Knudsen number and a pore diameter. The minimum Knudsen number line constrained by a packing fraction in a typical curve also indicates a minimum gas apparent permeability when a pore diameter is less than 100 nm.