“…Experiments using transparent epoxy replicas and analog materials have provided the opportunity to study various aspects of flow through individual fractures that are relevant to gravity‐driven wetting front and infiltration instability (Nicholl et al, ), water film flow and fracture surface transmissivities (Tokunaga & Wan, ), preferential flow paths (Brown et al, ), nonwetting phase trapping (Pyrak‐Nolte et al, ), entrapped phase dissolution (Glass et al, ), displacement of water by air (Amundsen et al, ; Neuweiler et al, ), and the effect of changes in surface wettability on two‐phase saturated flow (Bergslien & Fountain, ). In the last few decades, X‐ray computed tomography (CT) imaging techniques have been utilized to map three‐dimensional internal structure of fractures and saturating fluids in actual fractured rock samples while assuming impermeable rock matrix (Alvarado et al, ; Arshadi et al, ; Bertels et al, ; Karpyn et al, ). In these experiments, it has been observed that fracture aperture geometry, initial saturation conditions, and wettability are the key factors that control snap‐off and trapping of the nonwetting fluid, formation of preferential flow paths, and fluid distribution in the fractures (Karpyn et al, ).…”