Observations of nonwetting phase snap-off during drainage

Abstract

We study quasi-static drainage displacement experiments in Bentheimer sandstone micro-cores using X-ray computed microtomography. Two nonwetting fluids, air and n-decane, are investigated, under high and low flow rate conditions. Experimental conditions consider viscosity ratios that vary by a factor of 40, and capillary numbers that range five orders of magnitude; but all experiments investigated are conducted under nominally capillary-dominated conditions, indicating that drainage displacements should demonstrate percolation-like invasion patterns. However, we observe significant and prevalent snap-off of nonwetting phase under all experimental conditions, a phenomena not predicted by the conceptual model of percolation invasion. We further observe that the size and persistence of snapped-off ganglia are influenced by the experimental flow rate and the nonwetting phase fluid. The quasi-static experimental observations are supported by lattice-Boltzmann modelling of drainage dynamics. These findings indicate that current conceptual models of drainage are incomplete, with implications for future experimental and modelling studies as well as engineering applications. Show more