A cross-scale characterization of porous rocks altered by flow and dissolution

Flow and dissolution induce wormholes in porous rocks, which lead to a substantial increase in both permeability and flow heterogeneity of the rock formation. Wormholes originate from the initial micron-scale pore networks, and gradually transition to more prominent millimeter-scale holes. Wormholes have a crucial impact on the flow and reactions in subsurface technologies, such as critical mineral leaching, CO₂ storage and reservoir stimulation. Understanding how wormholes form from pore networks is crucial for the effectiveness of these subsurface technologies. However, current studies are limited to two separate scales of characterizations: millimeter-scale wormholes and micron-scale pore networks. The transitional region, which bridges these features at the two scales, remains largely unexplored and inadequately characterized. This knowledge gap obscures our understanding of the underpinning physics that governs wormhole formation in porous rocks. In this study, we aim to bridge these two scales of study with multiscale characterization. We create wormholes in porous gypsum specimens through core flood tests. The wormholes are then scanned with low-resolution (26.70 µm) and high-resolution (3.43 µm) X-ray computed tomography (CT). We quantitatively characterize the geometry of the wormholes leading to pore networks regarding their diameters, and quantities. This 3D cross-scale characterization allows for an accurate depiction of the interactions between wormholes and pore networks and provides physical insights into the initiation of wormholes.