Shale hydration is a critical factor influencing wellbore stability. However, accurately quantifying hydration strain and tracking the dynamic migration of fluid imbibition fronts in tight matrices remains a significant challenge. To address this issue, we propose a high-spatial-resolution monitoring scheme based on distributed fiber optic sensing (DFOS). By applying a hydrophobic coating to alter the imbibition path, we established a one-dimensional (1D) unidirectional imbibition boundary condition and compared it with semi-immersed free imbibition. Representative shale specimens with varying geological characteristics were tested to capture the continuous spatiotemporal evolution of hydration strain under both conditions. Our results show that under the restricted 1D path, the onset of strain exhibits a regular sequential delay along the fluid invasion direction, successfully mapping the progressive advancement of the imbibition front. The comparison between specimens with and without hydrophobic coating confirms that the coating effectively alters the imbibition path, leading to pronounced spatial lag and amplitude attenuation due to gravity and viscous resistance. Furthermore, we identify a dual characteristic of hydration strain. On one hand, governed by intrinsic properties such as clay content and permeability, different specimens exhibit distinctly different strain morphologies. On the other hand, within the same specimen, strain profiles at different measurement locations display high temporal self-similarity and spatial similarity, reflecting the structural control of the rock matrix. These findings suggest that shale hydration is a highly heterogeneous process, and the morphological differences can, to some extent, reflect variations in rock structure. Overall, this study provides an important methodological reference for improving wellbore stability models and optimizing drilling fluid design in deep shale engineering.
Sun et al. (Thu,) studied this question.