Mixed imbibition controls the advance of wetting fluid in multiscale geological media

Imbibition plays a central role during multiphase flows in geological media; yet, our understanding of imbi-bition dynamics across the multiscale features of rocks, including fractures, microcracks, and heterogeneous matrices is limited. Here, we deployed a unique combination of micro-and clinical X-ray CT imaging to probe directly the spatiotemporal evolution of imbibition in a natural, multiscale shale sample. The method enabled unraveling of mixed imbibition behavior, with spontaneous imbibition rates in the matrix pores and microcracks driven by capillarity proceeding as proportional to t-1/2, whereas pressure-driven flows in the macroscopic fractures yield apparent imbibition rates with proportional to t-1 scaling. Regardless of the aperture, we showed that spontaneous imbibition proceeds uniformly away from the fractures. The effects of microcracks are further investigated by comparing the dynamics of the imbibition fronts with and without microcracks. These results highlight the paramount role of microcracks on anomalous front roughening and the need to account for microcracks appropriately in the development of predictive theoretical models.

Automated summary

This study used micro-and clinical X-ray CT imaging to directly probe the spatiotemporal evolution of imbibition in a natural, multiscale shale sample, revealing the complexity of imbibition behavior and the significant impact of microcracks on the imbibition fronts. This highlights the importance of appropriately accounting for microcracks in the development of accurate predictive theoretical models.