Coupling effects of temperature, confining pressure, and pore pressure on permeability and average pore size of Longmaxi shale

Abstract

The evolution due to temperature and pressure of shale reservoir permeability affects the productivity evaluation and development decision of shale gas reservoirs, which is very important for the exploration and development of unconventional gas reservoirs. This study analyzed the coupling effects of temperature (25, 50, and 75°C), effective stress (15 and 30 MPa), and pore pressure (0.5, 2.0, 4.0, and 8.0 MPa) on the permeability of the shale sample in the Longmaxi Formation. As the temperature and pressure increased, the apparent permeability exhibited a downward trend, and the absolute permeability decreased with the rise of temperature or effective stress. An in-depth analysis of the gas slippage factors under the conditions of different temperature and pressure was conducted to evaluate the trend of the average pore width with temperature and pressure. The results were then verified by scanning electron microscopy (SEM). The results provide new insights into evaluating the permeability of the Longmaxi shale and can be used to enhance the gas recovery rate of deep shale gas reservoirs.