Dynamic evolution of shale permeability under coupled temperature and effective stress conditions

The permeability of shale in unconventional subsurface reservoirs under high-temperature and high effective stress conditions is of great significance for evaluating the extraction efficiency of shale gas and determining reservoir development programs. In this study, a series of permeability experiments using nitrogen gas were conducted on a sample from the lower Longmaxi Formation over a range of temperature (25-100 degrees C), effective stress (22.5-52.5 MPa), and pore pressure (0.5-8 MPa) conditions. The dynamic relationships between perme-ability and temperature, effective stress, and pore pressure are analyzed in detail. The results show that the apparent permeability decreases approximately linearly with increasing pore pressure, temperature, and effec-tive stress. The absolute permeability also decreases with increasing temperature or effective stress. Upon increasing the reservoir depth by 1000 m, the permeability decreases by an average of approximately 25%. Approximately two-thirds of this decline is caused by changes in the effective stress and approximately one-third by changes in temperature. The Klinkenberg parameter is also found to be positively correlated with temperature and effective stress. The results herein provide important guidance for evaluating permeability changes and the extraction efficiency for deep shale gas development.

Automated summary

In this study, permeability experiments were conducted on a shale sample from the lower Longmaxi Formation under various temperature, effective stress, and pore pressure conditions. The results showed that the permeability decreases linearly with increasing pore pressure, temperature, and effective stress. The absolute permeability also decreases with increasing temperature or effective stress. The Klinkenberg parameter was found to be positively correlated with temperature and effective stress. These findings provide important guidance for evaluating permeability changes and optimizing shale gas extraction efficiency in deep reservoirs.