The role of moisture adsorption in wellbore stability of shale formations: Mechanism and modeling

摘要

Understanding the interaction of drilling fluid with a shale formation is a critical step to properly describe pore pressure distribution, which directly affects wellbore stability. In this study, the moisture adsorption to shale surfaces is investigated to identify the proper isotherm type curve. It is shown that the moisture content of shale is correlated with water activity using a multilayer adsorption theory. It is found that the GAB model (developed by Guggenheim, Anderson and De Boer) fairly well describes the adsorption process for the selected shale types. Accordingly, the moisture content is correlated with water activity through the GAB model, which is incorporated into the transport equations. The adsorption parameter signifies the characteristic of a specific shale that interacts with aqueous fluids and can be introduced as an index to characterize different shale formations.