Combining macro and micro experiments to reveal the real-time evolution of permeability of shale

This research analyzed the real-time evolution of shale permeability using a combination of micro and macro experiments. The macro permeability experiment adopted the steady-state method and considered a particular stress path to study the influence of osmotic pressure, pore pressure, and confining pressure on the real-time evolution of permeability. The mechanism of the slippage effect on permeability evolution was studied using microscopic observations. The macro experiment results showed that: (1) permeability decreased as a concave power function with the increase of osmotic pressure; (2) permeability increased as a positive exponential function with an increase in mean pore pressure; (3) permeability decreased as a negative exponential function with an increase in confining pressure; (4) a multiple regression function was established to quantitatively describe the permeability evolution under the combined effect of the confining pressure and pore pressure. Furthermore, increasing the back pressure reduces the osmotic pressure and can effectively weaken the slippage effect, indicating that the back pressure has an essential effect on permeability evolution. The slip and transition flow, which account for a large proportion of all flow patterns, play a significant role in the slippage effect on permeability.