Relating Structural Elements to Cross-fault Flow - Implications for Fault Permeability Estimation

The evolution of cross-fault fluid flow in sand-clay sequences, especially the role of structural elements is not well understood. We present observations from analogue experiments using an underwater sandbox setup that allows dynamic cross-fault flux measurements. We combine the results of flux measurements with observations of the evolving fault zone in map view as well as with structural information of the clay smear after completing deformation. Carefully excavating the clay smear allows finding holes in the clay as well as relays, horses and other structures. Clay veneers of ~0.1 mm remain intact during the excavation process. We present results of eight experiments with the same total clay volume, of which three experiments had two clay layers with each half the thickness of the other experiments. The results show a more linear evolution of flux with smaller total flux. In experiments with a single clay layer we interpret the initial deformation to be hybrid failure with sudden increase of flux while at later stages fault segmentation and shearing of clay fragments causes less distinct increases of flux. Finally, we observe a process potentially capable of resealing discontinuous clay smears.