Abstract:

The slip effect can significantly enhance the permeability of fractured rock, and understanding its influence is crucial for comprehending gas flow dynamics within reservoirs. Most existing theoretical models treat intrinsic permeability and slip coefficient as constants and lack a method to define the critical pore pressure where the slip effect becomes significant. Thus, a dynamic apparent permeability model was developed based on equivalent fracture and rock bridge models, considering slip coefficient and intrinsic permeability as functions of effective stress and adsorption swelling. Using the established dynamic apparent permeability model, we analyzed variations in intrinsic permeability and slip coefficient under different confining stresses and permeable media. Additionally, we introduced the concept of the slip effect contribution rate to identify the critical pore pressure where the slip effect becomes significant. The results indicate that: 1) Intrinsic permeability increases with rising pore pressure, while slip coefficients decrease;   2) For different permeable media, the increase in intrinsic permeability with pore pressure is linked to gas adsorption properties, and slip coefficient variation is more complex; 3) A power function relationship exists between the slip effect contribution rate and pore pressure, with the critical pore pressure order being N₂<CO₂<He. This study offers theoretical guidance for predicting permeability and extracting resources from fractured rocks.

Key words: slip effect, confining stress, permeable media, critical pressure, permeability