title: Capillary saturation and desaturation.
abstract: Capillary desaturation experiments produce disconnected (trapped) ganglia of mesoscopic sizes intermediate between pore size and system size. Experimental evidence for interactions between these mesoscale clusters during desaturation is analyzed and discussed within the established microscopic and macroscopic laws of Newton, Young-Laplace, and Darcy. A theoretical expression for capillary number correlations is introduced that seems to have remained unnoticed. It expresses capillary desaturation curves in terms of stationary capillary pressures and relative permeabilities. The theoretical expression shows that the plateau saturation in capillary desaturation curves may in general differ from the residual nonwetting saturation defined through the saturation limit of the main hysteresis loop. Hysteresis effects as well as the difference between wetting and nonwetting fluids are introduced into the analysis of capillary desaturation experiments. The article examines experiments with different desaturation protocols and discusses the existence of a mesoscopic length scale intermediate between pore scale and sample scale. The theoretical expression is derived entirely within the existing traditional theory of two-phase flow in porous media and compared to a recent experiment.
authors.affiliation: ICP, Universität Stuttgart, 70569 Stuttgart, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Hilfer
authors.affiliation: School of Petroleum Engineering, University of New South Wales, NSW, 2052 Sydney, Australia.
authors.forename: R T
authors.initials: RT
authors.lastname: Armstrong
authors.affiliation: Shell Global Solutions International B.V., 2288 GS Rijswijk, Netherlands.
authors.forename: S
authors.initials: S
authors.lastname: Berg
authors.affiliation: Shell Global Solutions International B.V., 2288 GS Rijswijk, Netherlands.
authors.forename: A
authors.initials: A
authors.lastname: Georgiadis
authors.affiliation: Shell Global Solutions International B.V., 2288 GS Rijswijk, Netherlands.
authors.forename: H
authors.initials: H
authors.lastname: Ott