title: Beyond Darcy's law: The role of phase topology and ganglion dynamics for two-fluid flow.
abstract: In multiphase flow in porous media the consistent pore to Darcy scale description of two-fluid flow processes has been a long-standing challenge. Immiscible displacement processes occur at the scale of individual pores. However, the larger scale behavior is described by phenomenological relationships such as relative permeability, which typically uses only fluid saturation as a state variable. As a consequence pore scale properties such as contact angle cannot be directly related to Darcy scale flow parameters. Advanced imaging and computational technologies are closing the gap between the pore and Darcy scale, supporting the development of new theory. We utilize fast x-ray microtomography to observe pore-scale two-fluid configurations during immiscible flow and initialize lattice Boltzmann simulations that demonstrate that the mobilization of disconnected nonwetting phase clusters can account for a significant fraction of the total flux. We show that fluid topology can undergo substantial changes during flow at constant saturation, which is one of the underlying causes of hysteretic behavior. Traditional assumptions about fluid configurations are therefore an oversimplification. Our results suggest that the role of fluid connectivity cannot be ignored for multiphase flow. On the Darcy scale, fluid topology and phase connectivity are accounted for by interfacial area and Euler characteristic as parameters that are missing from our current models.
authors.affiliation: School of Petroleum Engineering, University of New South Wales, Sydney 2033, Australia.
authors.forename: Ryan T
authors.initials: RT
authors.lastname: Armstrong
authors.affiliation: Advanced Research Computing, Virginia Tech, Blacksburg, Virginia 24061, USA.
authors.forename: James E
authors.initials: JE
authors.lastname: McClure
authors.affiliation: Oak Ridge National Laboratory, Tennessee, Oak Ridge 37831, USA.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Berrill
authors.affiliation: Imperial College, London SW7 2AZ, United Kingdom.
authors.forename: Maja
authors.initials: M
authors.lastname: Rücker
authors.affiliation: Helmholtz-Centre for Environmental Research - UFZ, Theodor-Lieser-Str. 4, 06120 Halle (Saale), Germany.
authors.forename: Steffen
authors.initials: S
authors.lastname: Schlüter
authors.affiliation: Shell Global Solutions International B.V., Rijswijk, Kesslerpark 1, 2288 GS Rijswijk (Zh), The Netherlands.
authors.forename: Steffen
authors.initials: S
authors.lastname: Berg